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MAX-DOAS IO and BrO measurements in the western pacific boundary layer

MAX-DOAS IO and BrO measurements in the western pacific boundary layer. Enno Peters 1 , Katja Grossmann 2 , Folkard Wittrock 1 , Udo Frieß 2 , Anja Schönhardt 1 , Andreas Richter 1 , John P. Burrows 1 , Kirstin Krüger 3 , Birgit Quack 3 EGU Vienna, 05.04.2011

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MAX-DOAS IO and BrO measurements in the western pacific boundary layer

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  1. MAX-DOAS IO and BrO measurements in the western pacific boundary layer Enno Peters1, Katja Grossmann2, Folkard Wittrock1, Udo Frieß2, Anja Schönhardt1, Andreas Richter1, John P. Burrows1, Kirstin Krüger3, Birgit Quack3 EGU Vienna, 05.04.2011 1 Institut für Umweltphysik, Universität Bremen 2 Institut für Umweltphysik, Universität Heidelberg 3 IFM GEOMAR, Kiel

  2. I. Introduction

  3. Introduction • Importance: • Ozone depletion due to catalytic IO reactions • Sources of IO: • 1. Organic sources emitting precursors and • photolysis • Seaweed • Phytoplankton, algae • (under ice spring bloom of ice algae • producing organohalogens) • 2. Other/Inorganic sources • (directly from sea salt? / direct emission of I2 • from ocean surface?) http://seaweed.ucg.ie http://en.wikipedia.org

  4. Introduction • Where has IO already been measured? • Measurements mostly in polar regions (e.g. Spitsbergen, Antarctica) and • coastal regions, (e.g. Mace Head (Ireland), Tenerife, Tasmania). Selected references: Wittrock et al., GRL, 2000 Friess et al., GRL, 2001 McFiggans et al., ACP, 2004 Peters et al., ACP, 2005 Saiz-Lopez et al., ACP, 2006 Saiz-Lopez et al., Science, 2007 Carpenter et al., Mar.Chem., 2007 Read et al., Nature, 2008 1 ppt 2 ppt 6 ppt 10 ppt 2,2 ppt 2,8 ppt Published maximum VMR 2,2 ppt 10 ppt Adapted from Anja Schönhardt University of Bremen, 2009

  5. Introduction • Satellites provide global • image of trace gases • But: Problems over • oceans due to low • albedo and spectral • structures from water • MAX-DOAS more • sensitive to tropospheric • absorbers • Opportunity to go there and check for the background (how much IO over • open ocean) 0 ? IO from satellite instruments  see poster session (Anja Schönhardt)

  6. MAX-DOAS measurements Multi Axis - Differential Optical Absorption Spectroscopy • Measuring spectra of scattered sunlight • Deriving trace gas columns and profiles from absorption features • High sensitivity for stratospheric absorbers during twilight ( am and pm values) Spectrometers Light Telescope unit Y-shaped optical fibre Scheme of a MAX-DOAS instrument

  7. MAX-DOAS measurements Multi Axis - Differential Optical Absorption Spectroscopy • Measuring spectra of scattered sunlight • Deriving trace gas columns and profiles from absorption features • High sensitivity for stratospheric absorbers during twilight ( am and pm values) • High sensitivity for tropospheric absorbers using off-axis measurements • Converting slant columns into vertical columns/profilesusing radiative transfer models Spectrometers Light Telescope unit Y-shaped optical fibre Scheme of a MAX-DOAS instrument

  8. The Bremen MAX-DOAS campaign instrument • Y-shaped optical fiber bundle in • UV-spectrometer: 315 – 384 nm • (0,033 nm/pixel, resolution ~ 0,4 nm) • Vis-spectrometer: 400 – 573 nm • (0,13 nm/pixel, resolution ~ 0,8 nm)

  9. II. Measurements & results

  10. DOAS IO fit Fit example from 14.10.2009, 3° elevation • Fitting window: • 417.5 – 438.2 nm •  Three IO absorption bands • Considered cross sections: • Ozone, NO2, IO, H2O, VRS, • Ring, Offset (straylight) • Other fit parameters: • Quadratic polynomial, • fixed daily reference spectrum at 45° SZA • (to avoid direct sunlight and saturation effects) 0.1 s exposure time 30 s integration time Slant column ~ 2.6*1013 molec/cm2 Fit error 13.7 %

  11. DOAS IO fit • IO Slant columns 13-14.10.2009 from • Heidelberg and Bremen instruments • Data plotted with error < 30%, 5° Elevation 5° Elevation Error < 30% Correlation 3° elevation: 72% 5° elevation: 67% • More frequent Heidelberg • data, because Bremen • performed much more angles • Heidelberg tends to be • a bit higher than Bremen Bremen Heidelberg (Local time)  For Heidelberg data & analysis see poster session (Katja Grossmann)

  12. IO slant columns IO slant colums in 1°, 6°,15° Error < 30%   (Local time) • Slant columns separated under clear weather • conditions (due to different light path) •  contain information about profile • Using the profile retrieval BREAM (OEM)

  13. IO volume mixing ratios Example day: 14.10.2009 (Day with good weather conditions/sight) 14.10.2009

  14. IO volume mixing ratios Mixing Layer Height, 14.10.2009 (from radiosondes measurements) Time of MAX-DOAS measurements  ~ 500 – 800 m Vertical averages during the day: Lowest 800 m: 0.4 – 0.8 ppt Lowest 500 m: 0.4 – 0.9 ppt Lowest 200 m: up to 1.1 ppt (Local time)

  15. IO volume mixing ratios Lowest 800 m (Local time) • Mean VMR in MBL (assumed to be): • 0-800 m : Range between 0.4 – 0.9 ppt

  16. Complementary data (Local time) Highest IO values over open ocean at low chlorophyll content  No biogenic release source Map kindly provided by Tilman Dinter, IUP Bremen

  17. BrO results • BrO only detected three times (Oct 20, 21, 22), • most reliable at Oct 21 afternoon Slant Colums in 1°,4°,8° Errors < 30 % (Local time)

  18. BrO results • BrO only detected three times (Oct 20, 21, 22), • most reliable at Oct 21 afternoon • Viewing angles not well separated • Profiling with RTM not useful Slant Colums in 1°,4°,8° Errors < 30 % (Local time)

  19. BrO results • Simple geometric approach: • Assuming BrO in 1000 m box profile: Slant Colums in 1°,4°,8° Errors < 30 % (Local time) Map provided by Tilman Dinter, IUP Bremen

  20. III. Summary

  21. Summary • Remote sensing IO and BrO measurements have been performed over the • western pacific ocean during the TransBrom campaign. • In contrast to expectations, IO shows highest concentrations over open ocean • (0.4 to 1.1 ppt) at low chlorophyll content, no reliable observation in coastal regions. • No tropospheric BrO found, only three “events” in the coral sea at late • afternoon/evening local time. • As profiling is not possible, a rough estimation gives about 1 ppt BrO assuming a • 1000 m thick box profile. • For further interest see at poster session: • “Shipborne MAX-DOAS Measurements of Reactive Halogen Species over the • Western Pacific and the Eastern North Atlantic” (Katja Grossmann) • “Analysing satellite data for IO vertical columns in polar and tropical regions” • (Anja Schönhardt)

  22. Thank you!

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